Electrical stimulation of the heart is well known and has been utilized to overcome numerous deficiencies in the natural stimulation of the heart. Such external cardiac stimulation requires a reliable means for connecting electrical signals from a pulse generator, or pacer, to a particular region of the wall of the heart. For example, certain types of cardiac pacing lead are connected to the pacer, extend into the heart and are placed in contact with the inside wall of the right ventricle. These leads normally take the form of long, generally straight, flexible, insulated conductors having one end electrically connected to the pacer and the other end connected to an electrode. The electrode is placed in contact with a wall of the heart.
In order to stimulate the ventricle, the pacing lead is inserted into a blood vessel and is then pushed into the lower chamber of the heart, or ventricle. The end of the lead extends along a generally straight line and the electrode rests against the wall of the ventricular cavity. With this arrangement, there is little likelihood that the lead will fall out of this cavity.
On the other hand, a pacing lead which is used for stimulation of the atrium must be formed into a generally J-shaped configuration so that when the lead is inserted into the blood vessel, the lead may be positioned to curve up into the atrial cavity. Another problem associated with placing a pacing lead in the atrium is caused by the fact that the atrium has relatively smooth wall surfaces. With these smooth surfaces, it is difficult to retain the electrode in a fixed position with respect to the wall of the atrium.
Accordingly, one problem with prior pacing leads is that such devices have not been suitable for pacing the atrium. One technique for forming a pacing lead into a generally curved configuration is disclosed in U.S. Pat. No. 3,729,008, issued on Apr. 24, 1973. With the pacing lead disclosed in that patent, the cross-sectional area of the insulation surrounding the electrical conductor is modified in the region of the curved portion of the lead in order to cause the lead to remain in a curved configuration.
The present invention utilizes a curved, flattened spring which is embedded within the pacing lead for maintaining the lead in a curved configuration without the requirement of increasing the diameter of the lead in the curved region of the lead. The curved, flattened spring also imparts substantial torsional rigidity to the lead.